The demand for lower purity oxygen is increasing in applications such as glassmaking, steelmaking and energy production. Lower purity oxygen is generally produced in large quantities by the cryogenic rectification of feed air in a double column wherein feed air at the pressure of the higher pressure column is used to reboil the liquid bottoms of the lower pressure column and is then passed into the higher pressure column.
Some users of lower purity oxygen, for example integrated steel mills, often require some higher purity oxygen in addition to the lower purity oxygen. Such dual purity production cannot be efficiently accomplished with a conventional lower purity oxygen plant.
Accordingly, it is an object of this invention to provide a cryogenic rectification system which can effectively and efficiently produce both lower purity oxygen and higher purity oxygen.